114 REPORT— 1839. 



The vertebrae have their bodies more compressed in the an- 

 tero-posterior direction than in most other Ichthyosauri. From 

 the occiput to the iliac bones I count 45 vertebrae, and thence to 

 the end of the tail 75 vertebrae, making in all 120. From the 

 dentata to the 25th vertebra inclusive, the centrum is charac- 

 terized by two well-marked tubercles on each side for the arti- 

 culation of the ribs. It is one of these vertebrae which is figured 

 (in the inverted position with the spinal canal downwards) in 

 PI. XIV. of the Philosophical Transactions (1816), illustrative 

 of Sir E. Home's second memoir on the Ichthyosaurus. The 

 remaining vertebral centres present only a single surface for the 

 articulation of the rib : the spinous processes are thicker, shorter, 

 and more rounded superiorly, than in the Ich. intermedins or Ich. 

 communis : their articular processes for mutual interlocking are 

 well developed, especially at the anterior part of the spine. 



The ribs commence, as usual, at the second cervical vertebra ; 

 they increase in length to the twenty-fifth, and thence diminish, 

 at first gradually, but after the fortieth more suddenly. The 

 forty-fourth pair is straight, and they are continued, gradually 

 diminishing in length, attached by a simple head to the rudi- 

 mental transverse process on each side of the body of the verte- 

 bra, as far as the 100th vertebra, counting from the atlas. 



Pectoral Extremity, — The scapula* is a strong bone, with the 

 upper or dorsal extremity truncated and slightly expanded, the 

 anterior margin nearly straight, but slightly produced at its 

 distal end ; the posterior margin is slightly convex in the middle, 

 moderately concave above, and very concave below ; the inferior 

 extremity is expanded to receive the articular ends of the cora- 

 coid bone and humerus; the posterior part of this articular 

 extremity is the thickest part of the bone. 



The coracoid has a more extended scapulo-humeral surface, — 

 the scapular portion being the shortest, and has a narrower and 

 deeper upper notch, than in the other species of Ichthyosauri. 

 The internal surface of this bone is flat, but slightly concave 

 below ; the ento-sternal margin is thickened, the external sur- 

 face is slightly convex. In Lord Cole's collection there is the 

 coracoid of an Ichthyosaurus platyodon from Lyme, of which 



* The following are the words in which two great comparative anatomists 

 have recorded their opinions respecting the present bone when first presented 

 to their consideration in a detached siate. Sir E. Home, by whom it was first 

 figured, says, {Phil. Trans., 1818,) " It bears a greater resemblance to the first 

 bone of the paddle than to any other ; so that if the animal [meaning the Ich- 

 thyosaurus] has a posterior paddle this must belong to it." But the posterior 

 paddle of the Ichthyosaurus being subsequently discovered, by which the as- 

 sertion just quoted was disproved, Cuvier ventured an equally confident opinion 

 respecting it, and says, " C'est un humerus de plesiosaurus^ mais il ne resemble 

 pas entierement a ceux du squelette de Lyme." A lesson of caution in pro- 

 nouncing an opinion on a detached fossil bone is strongly inculcated by the ill 

 success which sometimes attends the guesses of even the best authorities. 



